The present invention relates to an on-demand type ink-jet recording device and, in particular, to a technique for driving a recording head of an on-demand type ink-jet recording device.
A conventional on-demand type of ink-jet recording device has a recording head which includes a plurality of pressure generation chambers for generating an ink pressure by means of piezoelectric vibrators or heating elements, a common reservoir for supplying ink to the respective pressure generation chambers, and nozzle openings communicating with the respective pressure generation chambers. In the recording head a drive signal is applied to the pressure generation chambers corresponding to a print signal to thereby jet out ink droplets from the nozzle openings onto a recording medium.
Such an ink-jet recording head can be classified into two types: one a bubble-jet type in which a resistance wire, as pressure generation means, generates Joule heat in a pressure generation chamber responsive to a drive signal, and the other a piezoelectric vibration type in which part of a pressure generation chamber is formed by a diaphragm and the diaphragm is compressed and shifted by means of a piezoelectric vibrator.
Since the former type utilizes the vapor pressure of the ink solvent vaporized instantaneously due to the heat generation of the resistance wire, only a small quantity of ink in the form of droplets can be jetted out, which makes it possible to realize printing at a high resolution as well as quick drying of the ink droplets. However, the heat generation of the resistance wire can cause the ink and recording head to deteriorate in quality readily.
According to the latter type, since no heat is generated, the quality of the ink is not deteriorated, the recording head has a longer permanent life, and operating costs are low. On the other hand, since a sufficient volumetric change is required to allow the generation of the ink droplets, the quantity of the ink droplets is great and the time necessary to dry the ink droplets is long.
Also, in the latter type, due to the fact that the volume of the pressure generation chamber is abruptly changed to thereby generate pressure, the ink is caused to fly in a column-like stream (similar to water shot from a water pistol), so that there is a time difference or a speed difference between the leading and trailing end portions of the flying ink, with the result that unwanted small ink droplets are generated, causing the printed dot to be distorted.
In order to solve the above-mentioned problems, as disclosed in Japanese Patent Publication No. Sho. 59-133067, there has been proposed a technique in which, after application of a drive signal to generate ink droplets, an auxiliary pulse is applied at a predetermined time instant to thereby forcibly stop the jetting-out of the ink in order to reduce the size of the ink column.
According to this technique, the generation of the small ink droplets incidental to the tail end of the ink column is prevented, that is, the generation of so-called "satellite" ink droplets is prevented, so that the printed dots can be made circular.
However, in this technique, since it is necessary to generate two types of pulses, that is, the drive pulse and auxiliary pulse at respective timings, the structure of the drive circuit is complicated. Also since the piezoelectric vibrator is driven against the inertia of a member forming a pressure generation chamber, a high force acts on the piezoelectric vibrator and the pressure generation chamber forming member, which results in a reduced life of the recording head.